Scientists to Watch Historic Venus Transit of the Sun from Alaska

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A NASA sun-watching spacecraft will have an unbeatable view of
June's historic Venus transit, but some of the probe's scientists
are taking measures to get a great look for themselves here on
Earth, too.

NASA's Solar Dynamics Observatory (SDO) satellite will watch from
space as Venus crosses the sun's face on June 5 (June 6 in the
Eastern Hemisphere) — the last such
Venus transit until December 2117. Not content to live
vicariously through their spacecraft, some SDO scientists are
headed to Alaska to watch the seven-hour event in its entirety.

"For the United States, only Hawaii and Alaska will
see the entire transit," said SDO project scientist Dean
Pesnell, of NASA's Goddard Space Flight Center in Greenbelt, Md.
"There's a solar physics meeting in Anchorage, Alaska, the week
after the transit. So we said, 'Well, let's go to Alaska and see
the transit.'"

A historic event

Venus transits occur in pairs that are eight years apart,
but these dual events take place less than once per century. The
last transit happened in 2004, and the next won't come until
2117. So next month's transit is the last chance for skywatchers
to see Earth's so-called sister planet trek across the solar
disk. [ Venus
Transit of 2004: 51 Amazing Photos ]

Venus transits have played a large role in astronomical
history. Scientists and explorers, for example, mounted large
expeditions to observe the 18th century's two transits, which
occurred in 1761 and 1769.

The idea was to time the Venus transit precisely from many
different spots around the globe, then use the principle of
parallax to calculate the distance from Earth to the sun — a
quantity that had eluded scientists for millenia. With that
information in hand, the scale of the entire
solar system would follow.

The 1761 and 1769 efforts both came up short, but measurements
made with the help of photographs during the 19th century's Venus
transits finally gave researchers the data they needed.

For its part, SDO will observe the transit to learn more about
Venus' atmosphere and to help calibrate some of its instruments,
Pesnell said.

An outreach opportunity

Pesnell and his colleagues plan to watch the transit from
Fairbanks, and they're going to use the rare event as an
education and outreach opportunity.

"We're working with some amateur astronomers up there to set up a
family science-oriented event in the city of Fairbanks," Pesnell
told SPACE.com, adding that the team will bring 10 to 20
different displays to teach people about the sun and SDO. "It's
been a fairly popular thing to take to cities."

Those of us unable to make the trek to Alaska, Hawaii or other
good transit-viewing locales around the world will still be able
to watch the historic event as it happens. Pesnell said that NASA
plans to webcast live footage of the transit from SDO, whose
images should be spectacular.

"There are no clouds in space, so we're guaranteed to have a
pretty good view," Pesnell said.

The $850 million SDO spacecraft launched in February 2010. The
probe's five-year mission is the cornerstone of a NASA science
program called Living with a Star, which aims to help researchers
better understand aspects of the sun-Earth system that affect our
lives and society.

You can follow SPACE.com senior writer Mike Wall on
Twitter:@michaeldwall.
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